The invention relates to a system for storing a pressurized gas in a motor vehicle, the system having a storage vessel and at least one thermally activatable safety valve for the evacuation of the storage vessel, which safety valve self-activates in the presence of a corresponding high temperature. The invention also relates to a method for the evacuation of a storage vessel for a pressurized gas in a motor vehicle.
In the context of alternative drive concepts, vehicles are increasingly being developed which are operated with gas, for example natural gas or hydrogen. Such vehicles require a storage vessel for the highly pressurized gas, and certain safety devices that ensure the pressure prevailing in the storage vessel does not reach the burst pressure of the vessel, in order to prevent bursting of the storage vessel.
For a fire situation, said storage vessels are further equipped with thermally activatable safety valves (Thermal Pressure Relief Devices, TPRD), which self-activate in the presence of a correspondingly high temperature, for example, by virtue of a closure compound melting. It can thus be achieved that the pressurized-gas storage vessel is evacuated before the vessel bursts owing to the excessively high internal pressure.
It is contemplated for the storage vessel to sustain prior damage, for example, in the event of an accident. This may lower the burst pressure of the storage vessel to below the operating pressure, or at least to below the triggering pressure of the safety devices that are provided, such that the damaged vessel constitutes a potential safety risk for as long as it is still pressurized. A pressurized-gas storage vessel of said type duly normally has so-called service valves by way of which manual evacuation is possible. But these service valves may, under some circumstances, be arranged on the vehicle at a poorly accessible location, or may be difficult to access as a result of the accident that has occurred. Also, a service function that may be provided for the release of pressure via a so-called service port may no longer be available in the event of an accident, owing to the elimination of the on-board electrical system.
It is therefore often not possible for the storage vessel to be targetedly evacuated, and for the system to thus be placed into a stable state, after an accident.
DE 10 2010 006 516 A1 has disclosed a generic system for storing a pressurized gas in a vehicle, wherein, in the event of an accident, an active safety system, which for example also triggers an airbag, transmits an activation signal to an evacuation device. The activation signal causes an explosive charge to be ignited, which may be arranged in the region of a thermally activatable safety valve, and the storage vessel is thus evacuated. Said document also discusses the possibility of the explosive charge being triggered from outside the vehicle by radio, wherein a radio transmitter carried by rescue forces transmits a signal to the vehicle safety system, which then generates the activation signal to the evacuation device.
A disadvantage of the described configuration is that, in the event of an accident-induced failure of the vehicle electronics, the possibility for the targeted evacuation of the pressurized-gas storage vessel no longer exists.
By contrast, the invention provides a system for storing a pressurized gas in a motor vehicle and a method for the evacuation of a storage vessel for a pressurized gas, in the case of which a targeted evacuation of the pressurized-gas storage vessel is reliably possible in a demand situation.
According to an aspect of the invention, in the case of a system of the type mentioned above, an additional, activatable evacuation device for the storage vessel is provided. The evacuation device has an interface for an external energy source, to which interface the external energy source can be connected for the purposes of targetedly evacuating the storage vessel. Thus, after an accident, regardless of the functional capability of the vehicle electronics, it is possible for the energy required for targetedly evacuating the storage vessel by way of the activatable evacuation device to be provided by connecting an external energy source (that is to say one which does not belong to the vehicle).
According to a further aspect of the invention, the additional evacuation device comprises a triggering device provided on the thermally activatable safety valve. The external energy source can be connected to the interface of the triggering device for the purposes of targetedly triggering the safety valve. Thus, use is made of the thermally activatable safety valve that is provided in any case, which safety valve, after connection of the external energy source, is triggered in targeted fashion and thus evacuates the storage vessel. A simple and thus inexpensive embodiment is obtained in this way.
It would alternatively be conceivable for an additional valve to be provided as evacuation device, which additional valve is arranged in parallel with respect to the thermally activatable safety valve and is activated by way of the external energy source.
The interface preferably has terminals, in particular, electrical terminals, for the external energy source. The terminals are arranged in a region of the motor vehicle that is accessible from the outside. This makes it possible, for example, for rescue forces to targetedly evacuate the pressurized gas in the storage vessel after an accident in order to prevent bursting of the storage vessel at a later point in time, for example, when the vehicle is transported away.
According to a further aspect of the invention, the external energy source can, after connection to the evacuation device, be externally activated in order to evacuate the storage vessel. In this way, the time of the evacuation can be precisely determined and targetedly delayed.
The activation is preferably performed by remote control, in particular, by radio or via an electrical ignition line. This makes it possible for the vehicle owner and other persons that are present to firstly move a safe distance away from the vehicle before the storage vessel is evacuated in targeted fashion.
If the evacuation device comprises a triggering device provided on the safety valve, the triggering device preferably has a thermal actuator, in particular, an electric heater. This may for example be in the form of a heating resistor and must be dimensioned such that the triggering temperature of the thermally activatable safety valve (approximately 105-110° C.) is reached, but not the ignition temperature of the gas.
According to a structurally simple aspect, the triggering device has a heating coil with which the thermally activatable safety valve is at least partially enwrapped. It may be provided that the safety valve as a whole is enwrapped, or that only a glass ampule belonging to the safety valve is enwrapped, with the heating coil and possibly insulated, self-evidently with a combustible material in order to ensure the functionality in the event of a fire. It would likewise be possible for the heating coil to be integrated into a wall of a glass ampule provided in the thermally activatable safety valve. In the two latter cases, less energy is required to activate the safety valve.
In an alternative embodiment, the evacuation device comprises a mechanical or pyrotechnic actuator. An example of a mechanical actuator is a piezo actuator which, when activated, destroys a glass ampule of the safety valve.
To prevent possible misuse, the terminals for the external energy source may be arranged in an interior compartment of the motor vehicle.
Alternatively or in addition, the evacuation device may have a breaker switch which is open during normal driving operation and which is closed by a crash signal from a vehicle safety system. Then, too, it is ensured that the evacuation device can be activated only in a demand situation, specifically, after an accident.
As already mentioned, the pressurized gas is in particular hydrogen or natural gas, preferably, compressed natural gas (CNG).
The objects of the invention are likewise achieved by way of a method for the evacuation of a storage vessel for a pressurized gas in a motor vehicle, which method is used in particular in a system of the type described herein. The method according to the invention has the following steps: an external energy source is, in a demand situation, connected to an evacuation device provided on the storage vessel, and the external energy source is activated for the purposes of targetedly evacuating the storage vessel by way of the evacuation device thus activated.
A “demand situation” is to be understood as including, for example, an accident. By contrast to an immediate activation of the evacuation device as a result of the accident event itself, for example, by way of an active vehicle safety system, the method according to the invention is distinguished by the fact that the storage vessel is evacuated only when there is a demand and after a time delay. Vehicle occupants can therefore firstly be rescued before gas emerges, which could ignite during the evacuation. The provision of the energy required for the evacuation device by way of an external energy source furthermore ensures that the evacuation of the storage vessel can be performed even if a vehicle-internal electrical supply fails.
According to an aspect of the method according to the invention, the evacuation device comprises a triggering device which is provided on a thermally activatable safety valve for the evacuation of the storage vessel, which safety valve self-activates in the presence of a correspondingly high temperature. The external energy source is activated in order to targetedly trigger the safety valve. Thus, the thermally activatable safety valve that is present in any case is utilized to permit targeted evacuation of the storage vessel in accordance with demand.
All of the aspects and advantages mentioned with reference to the system according to the invention likewise apply to the method according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.